There may exist a multi-RAT user equipment having capability of accessing at least two radio access technologies (RATs). In order to access a specific radio access technology (hereinafter abbreviated RAT), a connection to the specific RAT is established on the basis of a user equipment request and data transmission and reception may be then performed. Yet, even if the multi-RAT user equipment is capable of accessing at least two RATs, it is unable to access a plurality of RATs at the same time. In particular, currently, even if a user equipment has multi-RAT capability, it is unable to simultaneously perform data transmission/reception through different RATs.
The above-mentioned multi-RAT technology of the related art is a switching based multi-RAT technology. Since all transmitted data are transmitted in a manner of being switched to another RAT, the related art multi-RAT technology has a problem in selecting an RAT suitable for characteristics of a flow. However, a solution for this problem has not been proposed yet.